1. Field of the Invention
The present invention relates to liquid crystal compositions, liquid crystal devices, reflection display materials, light modulating materials, and anthraquinone compounds.
2. Description of the Related Art
Many types of liquid crystal devices (liquid crystal display devices) have been proposed. Because guest-host type liquid crystal devices use no polarizer, those of reflection type are expected to be bright image displays and those of transmission type are expected to be light modulating materials which are bright when they are transparent. In guest-host type liquid crystal devices, a dichroic dye is dissolved in a liquid crystal, and coloring and decoloring are switched by change in alignment of the dichroic dye synchronized with the movement of the liquid crystal due to an electric field.
The guest-host type device is described for example in “Handbook of Liquid Crystals”, written by B. Bahadur, edited by D. Demus, J. Goodby, G. W. Gray, H. W. Spiess, and V. Vill, Vol. 2A, published by Wiley-VCH, 1998, Chapters 3 and 4, pages 257-302. Dichroic dyes used in guest-host type liquid crystal devices are required to exhibit proper absorption properties, a high order parameter, a high solubility in host liquid crystal, durability, or the like.
From the viewpoint of dichroic ratio, solubility and durability, especially azo- and anthraquinone dichroic dyes have been investigated widely. However, azo dichroic dyes are defective in light resistance though they are good with respect to order parameter and solubility.
On the other hand, anthraquinone dyes have low solubility in host liquid crystals though they have high light resistance. In order to reconcile the solubility and the order parameter, many researchers have made various studies, e.g., introduction of a liquid crystalline substituent into an anthraquinone skeleton and increase in compatibility with liquid crystal. For example, Japanese Patent Application Laid-Open (JP-A) Nos. 58-57488, 1-252691, and 62-277471 can be referred to. However, the solubility is still unsatisfactory.